It's easy to create a double-exposure effect in GIMP. Try this:
http://iffles.com/2009/10/26/adding-a-texture-in-gimp/Also try color toning. Here's a tutorial about using curves to adjust colors:
http://blog.patdavid.net/2012/06/gettin ... urves.htmlA simpler way to adjust colors is to use a preset (after all, VSCO wants you to buy their film emulation presets). If you have G'MIC, take a look at the Film Emulation - Various filters. "Vintage Alt" or "Sunny" will add the soft warm tones and low contrast that I see in many of Mr. Venter's images.
http://gmic.sourceforge.net/film_emulat ... tml#browse